Brocade Virtual ADX Server Load Balancing Guide (Supporting ADX v03.1.00) - Manual (Page 79)

Brocade Virtual ADX Server Load Balancing Guide 63
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Configuring Direct Server Return
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Configuring L3 Direct Server Return
In an L3 DSR configuration, the Brocade Virtual ADX marks all packets sent to servers bound to a
specified VIP (the L3 DSR VIP) by setting the DSCP field to a configured value.
The real server must be programmed to check the DSCP field of incoming packets and change the
source IP address of appropriate reply packets from its own IP address (real IP address) to the
virtual IP address (VIP).
Three changes must be implemented to support L3 DSR:
• TOS marking of SLB and health check packets: All SLB and health check traffic sent to servers
bound to a specified VIP must be marked by a specific DSCP field value. Use the tos-marking
command to specify the DSCP field value.
• Special intelligence on real servers: The real server must be programmed to check the DSCP
field of incoming packets and change the source IP address of appropriate reply packets from
its own IP address (real IP address) to the virtual IP address (VIP).
• Special intelligence for handling health check responses: To enable the Brocade Virtual ADX to
correctly handle health check replies you must configure hc-l3-dsr under the VIP using the
tos-marking command with the hc-l3-dsr option.
TOS marking of SLB and health check packets
To configure the Brocade Virtual ADX for L3 DSR, the Brocade Virtual ADX must set the DSCP field
value in all packets sent to servers bound to a specified VIP.
Use the tos-marking command within a VIP configuration to specify the DSCP field value of traffic
packets send to real servers bound to a specific VIP.
Virtual ADX(config)#server virtual-name-or-ip vip1 10.10.1.151
Virtual ADX(config-vs-vip1)#tos-marking 18
Virtual ADX(config-vs-vip1)#bind http rs1 http
The Brocade Virtual ADX sets the DSCP field value to 18 in all packets sent to real server rs1.
Use the hc-l3-dsr option to ensure that Brocade Virtual ADX will process the health check reply
packets correctly:
Virtual ADX(config)#server virtual-name-or-ip vip1 10.10.1.151
Virtual ADX(config-vs-vip1)#tos-marking 18 hc-l3-dsr
Virtual ADX(config-vs-vip1)#bind http rs1 http
Although the Brocade Virtual ADX will have sent health check probes to the real server IP, it will
receive replies from the VIP. The hc-l3-dsr option ensures that responses from a different IP
address are handled correctly.
Syntax: tos-marking DSCP-value hc-l3-dsr
The DSCP-value variable specifies the value of the DSCP field that you want to send to all packets
sent to servers bound to the VIP.
With the hc-l3-dsr option configured the health check reply packets will be sent back to the VIP on
the Brocade Virtual ADX.